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A276322 Numbers k such that (13*10^k + 83) / 3 is prime.

%I A276322 #21 Jun 02 2024 14:03:24
%S A276322 1,2,5,7,17,18,25,60,64,66,118,125,1021,1901,2273,2524,6048,7098,8281,
%T A276322 11634,13843,16098,18652,18661,20570,32291,34181,59928,65297,86546
%N A276322 Numbers k such that (13*10^k + 83) / 3 is prime.
%C A276322 For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 3 followed by the digits 61 is prime (see Example section).
%C A276322 a(31) > 2*10^5.
%H A276322 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>.
%H A276322 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 43w61</a>.
%e A276322 5 is in this sequence because (13*10^5 + 83) / 3 = 433361 is prime.
%e A276322 Initial terms and associated primes:
%e A276322 a(1) = 1, 71;
%e A276322 a(2) = 2, 461;
%e A276322 a(3) = 5, 433361;
%e A276322 a(4) = 7, 43333361;
%e A276322 a(5) = 17, 433333333333333361, etc.
%t A276322 Select[Range[0, 100000], PrimeQ[(13*10^# + 83) / 3] &]
%o A276322 (PARI) is(n)=ispseudoprime((13*10^n + 83)/3) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y A276322 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K A276322 nonn,more
%O A276322 1,2
%A A276322 _Robert Price_, Sep 01 2016